Civil Engineering Reference
In-Depth Information
Table 7.12 Types of applications of RAC (BCSJ 1977, cited by Hansen
1992
)
Concrete type
Major application
I
Foundations of general buildings, floors of commercial
buildings and heavy foundations
II
Foundations for blocks of precast concrete, lightweight non-
residential buildings, machine foundations
III
Foundations of wood buildings, fixing fence and gates,
foundations of simple machines
ratio must be lower than 0.7 and the cement content should be equal to or greater
than 250 kg/m
3
. The amount of water used should be kept as low as possible and
similarly, the ratio of fine to coarse aggregate ratio should also be kept at a value
with which concrete with a minimum workability can be produced.
This specification makes no distinction between the nature and composition of
the aggregates to be used in the manufacture of concrete, as it does not prevent the
use of the recycled fine fraction. The maximum design strength of RAC is
determined by the type of RA used. Thus, RAC made with coarse RA is limited to
18 MPa and RAC made with both coarse and fine RA is limited to 12 MPa. In both
cases, concrete is only recommended for non-structural concrete, which is
somehow contradictory since the aggregate's requirements are quite demanding.
This conservative stance in terms of the use of RA may be due to the experimental
state-of-the-art when the document was put forward, in 1977, and a concern with
the intense seismic activity registered in Japan.
The coarse fraction in three types of concrete is entirely composed of RA while
fine RA can be used in different amounts. However, the application of RA is not
conditioning since the standard only considers concrete with very low compressive
strength. By comparison with other specifications, this one is conservative in terms
of some properties, which can prevent wide-scale application of RA. For example,
the RILEM (1994) specification on the use of RA in concrete allows using coarse
RA with density of 2,000 kg/m
3
in several high-quality concrete of strength
classes up to C50/60, while the Japanese standard only allows relatively high-
quality RA (with density of 2,200 kg/m
3
) to prepare very low-strength concrete.
There is presently a set of Japanese norms that regulate the use of RA in
concrete in a more up-to-date manner than the one mentioned in the previous
paragraph: JIS A 5021 (2005) RA for concrete—Class H, JIS A 5022 (2006) RA
for concrete—Class M, JIS A 5023 (2007) RA for concrete—Class L.
These documents establish a set of requisites imposed on aggregates, more
demanding for class-H concrete and less so for class-L concrete. These demands
are concomitant with the conditions of application of the concrete the aggregates
are incorporated into. Therefore JIS A 5023 regulates the application of RA in
non-structural concrete, JIS A 5022 scope is concrete unaffected by freeze-thaw
cycles and JIS A 5021 concerns the use of RA in high-performance concrete.
